Field of the Invention
The present invention relates to a liquid discharge head and a head unit using the same, and particularly, to a liquid discharge head that drives a piezoelectric element to discharge a liquid.
Description of the Related Art
Liquid discharge apparatuses that discharge a liquid, such as ink, onto a recording object to perform recording include a liquid discharge head in which a number of liquid discharge portions are arranged in two dimensions in order to perform higher-definition recording at high speed. Each liquid discharge portion has a pressure chamber including a discharge port, and pressure generating means that is provided to face the pressure chamber. It is also known that a piezoelectric element is used as the pressure generating means. Particularly, it is relatively easy to densely and precisely arrange bending-type piezoelectric elements in which the wall surface of a pressure chamber facing a discharge port is bent and deformed by a piezoelectric element and that increase and decrease the volume of the pressure chamber, and thus, the bending-type piezoelectric elements are widely used. In the liquid discharge portion of the liquid discharge head, there is a period of time for which a liquid is not discharged during operation. Even when recording is continuously performed, according to a drawing pattern to be printed, such as a blank, space, or the like of a recording object, there is a discharge port that does not discharge a liquid for a long time. During the time period in which the liquid is not discharged, the liquid in the vicinity of the discharge port may deteriorate due to evaporation, and consequently a discharge failure may occur. Therefore, in order not to use excessive time to restore the discharge port where the discharge failure has occurred, it is desired to prevent the discharge failure resulting from the evaporation or the like of the liquid.
A liquid discharge head in which an inlet end portion and an outlet end portion are provided in a pressure chamber of a liquid discharge portion is disclosed in Japanese Patent Application Laid-Open No. 2012-532772. A portion of the liquid that has flowed in from the inlet end portion is discharged from the discharge port by the operation of a bending-type piezoelectric element, and the remaining liquid is discharged from the outlet end portion. When a liquid is not discharged, the entire quantity of the liquid that has flowed in from the inlet end portion is discharged from the outlet end portion. Accordingly, the flowing of a liquid is always maintained within the pressure chamber to realize a so-called through-flow, irrespective of whether the liquid is discharged from the discharge port. Since the liquid does not easily stagnate in the vicinity of the discharge port, a discharge failure caused by the deterioration of the liquid does not occur easily. A liquid discharge head including two inlet end portions in one pressure chamber is disclosed in Japanese Patent Application Laid-Open No. 2012-006224.
In the liquid discharge head described in Japanese Patent Application Laid-Open No. 2012-532772, a plurality of the liquid discharge portions is connected to a common liquid supply flow path and a common liquid collection flow path. Therefore, the common liquid supply flow path and the common liquid collection flow path need to allow a total flow rate of liquid required for the plurality of liquid discharge portions connected thereto to flow therethrough. However, in the liquid discharge head in which the liquid discharge portions are arranged in high density, the flow path cross-sectional areas of the common liquid supply flow path and the common liquid collection flow path are liable to be limited. Particularly, in the liquid discharge head described in Japanese Patent Application Laid-Open No. 2012-532772, the shape of the pressure chamber is circular. Therefore, it is difficult to reduce the intervals of the pressure chambers adjacent to each other, and it is difficult to shorten the lengths of the common liquid supply flow path and the common liquid collection flow path. For this reason, the pressure gradient or pressure loss along the common liquid supply flow path and the common liquid collection flow path are liable to occur, and it is difficult to control the negative pressure of a liquid such that a uniform meniscus is formed in all of the discharge ports. Moreover, since the discharge port is located at the center of the circular pressure chamber, a flow velocity at the position of the discharge port is smaller than that at the other positions of the pressure chamber, and it is necessary to increase a flow rate in order to obtain the effects of the through-flow. However, if the flow rate is increased, the pressure loss resulting from the flow path resistances of the common liquid supply flow path and the common liquid collection flow path are further increased.
In order to solve this problem, as described in Japanese Patent Application Laid-Open No. 2012-006224, it is also considered that two common liquid supply flow paths are provided, and the flow rate of each common liquid supply flow path is suppressed. However, the supply of a liquid in Japanese Patent Application Laid-Open No. 2012-006224 does not relate to the through-flow. If the liquid discharge head in Japanese Patent Application Laid-Open No. 2012-006224 is used in order to realize the through-flow, it is necessary to separately provide a common liquid collection flow path. Therefore, the liquid discharge portions are not able to be arranged in high density.